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		<title>three.js webgl - shader - curvature [ninja]</title>
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			<a href="https://threejs.org" target="_blank" rel="noopener">three.js</a> - curvature estimation of a geometry<br/>
			by <a href="http://codercat.club" target="_blank" rel="noopener">CoderCat</a>
		</div>

		<script id="vertexShaderRaw" type="x-shader/x-vertex">

		attribute float curvature;

		varying float vCurvature;

		void main() {

			vec3 p = position;
			vec4 modelViewPosition = modelViewMatrix * vec4( p , 1.0 );
			gl_Position = projectionMatrix * modelViewPosition;
			vCurvature = curvature;

		}

		</script>

		<script id="fragmentShaderRaw" type="x-shader/x-fragment">

		varying vec3 vViewPosition;
		varying float vCurvature;

		void main() {
				gl_FragColor = vec4( vCurvature * 2.0, 0.0, 0.0, 0.0 );
		}

		</script>

		<script type="module">

			import * as THREE from '../build/three.module.js';

			import { GUI } from './jsm/libs/dat.gui.module.js';
			import { OrbitControls } from './jsm/controls/OrbitControls.js';
			import { OBJLoader } from './jsm/loaders/OBJLoader.js';

			let camera, scene, renderer;

			let ninjaMeshRaw, curvatureAttribute, bufferGeo;

			init();
			animate();

			//returns average of elements in a dictionary
			function average( dict ) {

				let sum = 0;
				let length = 0;

				Object.keys( dict ).forEach( function ( key ) {

					sum += dict[ key ];
					length ++;

				} );

				return sum / length;

			}

			//clamp a number between min and max
			function clamp( number, min, max ) {

				return Math.max( min, Math.min( number, max ) );

			}

			//filter the curvature array to only show concave values
			function filterConcave( curvature ) {

				for ( let i = 0; i < curvature.length; i ++ ) {

					curvature[ i ] = Math.abs( clamp( curvature[ i ], - 1, 0 ) );

				}

			}

			//filter the curvature array to only show convex values
			function filterConvex( curvature ) {

				for ( let i = 0; i < curvature.length; i ++ ) {

					curvature[ i ] = clamp( curvature[ i ], 0, 1 );

				}

			}

			//filter the curvature array to show both the concave and convex values
			function filterBoth( curvature ) {

				for ( let i = 0; i < curvature.length; i ++ ) {

					curvature[ i ] = Math.abs( curvature[ i ] );

				}

			}

			//initialize the scene
			function init() {

				scene = new THREE.Scene();

				camera = new THREE.PerspectiveCamera( 75, window.innerWidth / window.innerHeight, 0.1, 1000 );

				camera.position.x = - 23;
				camera.position.y = 2;
				camera.position.z = 24;

				renderer = new THREE.WebGLRenderer();
				renderer.setSize( window.innerWidth, window.innerHeight );
				renderer.autoClear = false;
				document.body.appendChild( renderer.domElement );

				const controls = new OrbitControls( camera, renderer.domElement );
				controls.minDistance = 20;
				controls.maxDistance = 100;

				const loader = new OBJLoader();
				//load the obj
				loader.load( 'models/obj/ninja/ninjaHead_Low.obj', function ( object ) {

					object.traverse( function ( child ) {

						if ( child.isMesh ) {

							bufferGeo = child.geometry;
							bufferGeo.center();
							const dict = {};

							for ( let i = 0; i < bufferGeo.attributes.position.count; i += 3 ) {

								//create a dictionary of every position, and its neighboring positions
								const array = bufferGeo.attributes.position.array;
								const normArray = bufferGeo.attributes.normal.array;

								const posA = new THREE.Vector3( array[ 3 * i ], array[ 3 * i + 1 ], array[ 3 * i + 2 ] );
								const posB = new THREE.Vector3( array[ 3 * ( i + 1 ) ], array[ 3 * ( i + 1 ) + 1 ], array[ 3 * ( i + 1 ) + 2 ] );
								const posC = new THREE.Vector3( array[ 3 * ( i + 2 ) ], array[ 3 * ( i + 2 ) + 1 ], array[ 3 * ( i + 2 ) + 2 ] );

								const normA = new THREE.Vector3( normArray[ 3 * i ], normArray[ 3 * i + 1 ], normArray[ 3 * i + 2 ] ).normalize();
								const normB = new THREE.Vector3( normArray[ 3 * ( i + 1 ) ], normArray[ 3 * ( i + 1 ) + 1 ], normArray[ 3 * ( i + 1 ) + 2 ] ).normalize();
								const normC = new THREE.Vector3( normArray[ 3 * ( i + 2 ) ], normArray[ 3 * ( i + 2 ) + 1 ], normArray[ 3 * ( i + 2 ) + 2 ] ).normalize();

								const strA = posA.toArray().toString();
								const strB = posB.toArray().toString();
								const strC = posC.toArray().toString();

								const posB_A = new THREE.Vector3().subVectors( posB, posA );
								const posB_C = new THREE.Vector3().subVectors( posB, posC );
								const posC_A = new THREE.Vector3().subVectors( posC, posA );

								const b2a = normB.dot( posB_A.normalize() );
								const b2c = normB.dot( posB_C.normalize() );
								const c2a = normC.dot( posC_A.normalize() );

								const a2b = - normA.dot( posB_A.normalize() );
								const c2b = - normC.dot( posB_C.normalize() );
								const a2c = - normA.dot( posC_A.normalize() );

								if ( dict[ strA ] === undefined ) {

									dict[ strA ] = {};

								}

								if ( dict[ strB ] === undefined ) {

									dict[ strB ] = {};

								}

								if ( dict[ strC ] === undefined ) {

									dict[ strC ] = {};

								}

								dict[ strA ][ strB ] = a2b;
								dict[ strA ][ strC ] = a2c;
								dict[ strB ][ strA ] = b2a;
								dict[ strB ][ strC ] = b2c;
								dict[ strC ][ strA ] = c2a;
								dict[ strC ][ strB ] = c2b;

							}

							let curvatureDict = {};
							let min = 10, max = 0;

							Object.keys( dict ).forEach( function ( key ) {

								curvatureDict[ key ] = average( dict[ key ] );

							} );

							//smoothing
							const smoothCurvatureDict = Object.create( curvatureDict );

							Object.keys( dict ).forEach( function ( key ) {

								let count = 0;
								let sum = 0;
								Object.keys( dict[ key ] ).forEach( function ( key2 ) {

									sum += smoothCurvatureDict[ key2 ];
									count ++;

								} );
								smoothCurvatureDict[ key ] = sum / count;

							} );

							curvatureDict = smoothCurvatureDict;

							// fit values to 0 and 1
							Object.keys( curvatureDict ).forEach( function ( key ) {

								const val = Math.abs( curvatureDict[ key ] );
								if ( val < min ) min = val;
								if ( val > max ) max = val;

							} );

							const range = ( max - min );

							Object.keys( curvatureDict ).forEach( function ( key ) {

								const val = Math.abs( curvatureDict[ key ] );
								if ( curvatureDict[ key ] < 0 ) {

									curvatureDict[ key ] = ( min - val ) / range;

								} else {

									curvatureDict[ key ] = ( val - min ) / range;

								}

							} );

							curvatureAttribute = new Float32Array( bufferGeo.attributes.position.count );

							for ( let i = 0; i < bufferGeo.attributes.position.count; i ++ ) {

								const array = bufferGeo.attributes.position.array;
								const pos = new THREE.Vector3( array[ 3 * i ], array[ 3 * i + 1 ], array[ 3 * i + 2 ] );
								const str = pos.toArray().toString();
								curvatureAttribute[ i ] = curvatureDict[ str ];

							}

							bufferGeo.setAttribute( 'curvature', new THREE.BufferAttribute( curvatureAttribute, 1 ) );

							//starting filter is to show both concave and convex
							const curvatureFiltered = new Float32Array( curvatureAttribute );
							filterBoth( curvatureFiltered );

							const materialRaw = new THREE.ShaderMaterial( {

								vertexShader: document.getElementById( 'vertexShaderRaw' ).textContent,
								fragmentShader: document.getElementById( 'fragmentShaderRaw' ).textContent

							} );

							ninjaMeshRaw = new THREE.Mesh( bufferGeo, materialRaw );

						}

					} );

					scene.add( ninjaMeshRaw );

				} );


				//init GUI
				const params = {

					filterConvex: function () {

						const curvatureFiltered = new Float32Array( curvatureAttribute );
						filterConvex( curvatureFiltered );
						bufferGeo.attributes.curvature.array = curvatureFiltered;
						bufferGeo.attributes.curvature.needsUpdate = true;


					},
					filterConcave: function () {

						const curvatureFiltered = new Float32Array( curvatureAttribute );
						filterConcave( curvatureFiltered );
						bufferGeo.attributes.curvature.array = curvatureFiltered;
						bufferGeo.attributes.curvature.needsUpdate = true;


					},
					filterBoth: function () {

						const curvatureFiltered = new Float32Array( curvatureAttribute );
						filterBoth( curvatureFiltered );
						bufferGeo.attributes.curvature.array = curvatureFiltered;
						bufferGeo.attributes.curvature.needsUpdate = true;

					}
				};

				const gui = new GUI();

				const topologyFolder = gui.addFolder( 'Topology' );
				topologyFolder.add( params, 'filterConvex' );
				topologyFolder.add( params, 'filterConcave' );
				topologyFolder.add( params, 'filterBoth' );
				topologyFolder.open();

				onWindowResize();

				window.addEventListener( 'resize', onWindowResize );

			}

			function onWindowResize() {

				renderer.setSize( window.innerWidth, window.innerHeight );
				camera.aspect = window.innerWidth / window.innerHeight;
				camera.updateProjectionMatrix();

			}

			function animate() {

				requestAnimationFrame( animate );

				render();

			}

			function render() {

				renderer.render( scene, camera );

			}

		</script>

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